Microwave guide

Abstract

A microwave guide suitable for carrying microwaves between an object that is vibrating that is connected to a first end of the guide and an object connected to the other end of the guide that is to be protected from transmitted vibrations, the guide providing a restricted path for the transmission of vibrations. In one embodiment, the guide has a flexible mesh part having an inner surface which has high electric conductivity and is provided with a plurality openings. The openings may be sufficiently small such that microwave radiation is unable to pass through the opening. The guide may also include a support structure which extends along the length of the guide. The support structure may have a low dielectric loss tangent and may be sufficiently rigid to provide support to the mesh part.

Claims

1. A microwave guide suitable for carrying microwaves between an object that is to be at least partially isolated from vibrations and that is connected to a first end of the microwave guide and an object that is vibrating that is connected to a second end of the microwave guide, the microwave guide providing a restricted path for the transmission of vibrations to the first end of the microwave guide from the second end of the microwave guide, the microwave guide comprising: a first flexible mesh part having an inner surface which has high electric conductivity and is provided with a plurality openings, each opening being sufficiently small that microwave radiation is unable to pass through, wherein the first flexible mesh part comprises a first flexible sleeve that extends along the length of the microwave guide, the first flexible support structure and first flexible sleeve being arranged concentrically around a common axis, and the first flexible sleeve being a loose fit around the first support structure; and a first flexible support structure which extends along a length of the microwave guide and which has a low dielectric loss tangent and which is sufficiently rigid to provide support to the first flexible mesh part, in which the first flexible mesh part comprises a braided, woven, knitted or otherwise interlaced material, which in use flexes as threads of the interlaced material slide over one another, or move relative to one another; a second flexible mesh part having an inner surface which has high electric conductivity and is provided with a plurality openings, each opening being sufficiently small that microwave radiation is unable to pass through, the second flexible mesh part being located outside of the first flexible mesh part; and a second flexible support structure which extends along the length of the microwave guide outside of the first flexible mesh part and inside of the second flexible mesh part and is provided with a plurality of openings, each opening being sufficiently small that microwave radiation is unable to pass through.

2. The microwave guide according to claim 1, wherein the microwave guide comprises only the first flexible sleeve.

3. The microwave guide according to claim 1, wherein an inner wall of the first flexible sleeve forms an inner wall of the guide microwave that the microwaves cannot pass through.

4. The microwave guide according to claim 1, wherein an outer sleeve and the inner mesh part each comprise a braided, woven, knitted or otherwise interlaced material which in use flexes as the threads of the interlaced material slide over one another, or move relative to one another and which may have high electric conductive surfaces.

5. The microwave guide according to claim 1, wherein the length of the microwave guide is (2n+1)/4 times a wavelength of microwave energy that is to be passed along the microwave guide when in use, where n is a whole number.

6. The microwave guide according to of claim 1, wherein the material of the first flexible mesh part is knitted, woven, braided or otherwise interlaced into a seamless tube.

7. The microwave guide according to claim 1, wherein the second flexible mesh part is knitted, woven, braided or otherwise interlaced into a seamless tube.

8. The microwave guide according to claim 7, wherein the material of one or both of the first flexible mesh part and the second flexible mesh part comprises a braided material in which threads are crossed so that some or all of the threads extend in a direction that is neither parallel to or orthogonal to the long axis of the sleeve.

9. The microwave guide according to claim 1, wherein the first flexible mesh part and first flexible support structure comprise a composite structure in which the first flexible mesh part is integral to and coaxial with the first support structure.

10. The microwave guide according to claim 1, wherein at least one of the first flexible support structure or second flexible support structure comprises at least one helical spring.

11. The microwave guide according to claim 10, wherein the first flexible support structure comprises a spring, such as a PTFE structure or other material that displays a low dielectric loss tangent at microwave frequencies.

12. The microwave guide according to claim 10, wherein the first flexible support structure is held under a load by being secured to one or more end flanges which are located at the end of the microwave guide.

13. The microwave guide according to claim 12, wherein the load is adjustable to vary the tension of the first flexible support structure.

14. The microwave guide according to claim 1, wherein when there is vibration of one end of the microwave guide at a frequency of 50 Hz the magnitude of the vibrations at the other end of the microwave guide will be attenuated by at least 11 dB (minus 11 decibels).

15. The microwave guide according to claim 1 further comprising an additional outer shell having a continuous sleeve of material that extends along the length of the microwave guide and which in use can be arranged to seal the first flexible mesh part within the shell.

16. The microwave guide according to claim 15, wherein the shell comprises a flexible bellows.

17. The microwave guide according to claim 1, wherein a launcher for launching microwaves into a vibrating object is provided, the launcher comprising a source of microwave radiation that is to be protected from vibrations from the vibrating object, and wherein the microwave guide is secured at one end to the source and at the other to the vibrating object, the microwave guide substantially preventing the transmission of vibrations from the vibrating object to the source of microwave radiations through the guide.

18. The microwave guide according to claim 17, wherein the microwave launcher includes a fan which blows air into the end of the guide connected to the source.

19. The microwave guide according to claim 17, wherein a vibrating receptacle suitable for use in drying feedstock in the receptacle using microwave energy that has passed through the microwave guide is provided, wherein the vibrating receptacle includes a receptacle and at least one actuator that causes the receptacle to vibrate at a known frequency at which the microwave guide provides a high degree of attenuation from one end to the other.

20. A microwave guide suitable for carrying microwaves between an object that is to be at least partially isolated from vibrations and that is connected to a first end of the microwave guide and an object that is vibrating that is connected to a second end of the microwave guide, the microwave guide providing a restricted path for the transmission of vibrations to the first end of the microwave guide from the second end of the microwave guide, the microwave guide comprising: a first flexible mesh part having an inner surface which has high electric conductivity and is provided with a plurality openings, each opening being sufficiently small that microwave radiation is unable to pass through, wherein the first flexible mesh part comprises a first flexible sleeve that extends along the length of the microwave guide, the first flexible support structure and first flexible sleeve being arranged concentrically around a common axis, and the first flexible sleeve being a loose fit around the first support structure; and a first flexible support structure which extends along a length of the microwave guide and which has a low dielectric loss tangent and which is sufficiently rigid to provide support to the first flexible mesh part, in which the first flexible mesh part comprises a braided, woven, knitted or otherwise interlaced material, which in use flexes as threads of the interlaced material slide over one another, or move relative to one another; a second flexible mesh part having an inner surface which has high electric conductivity and is provided with a plurality openings, each opening being sufficiently small that microwave radiation is unable to pass through, the second flexible mesh part being located outside of the first flexible mesh part; and a second flexible support structure which extends along the length of the microwave guide outside of the first flexible mesh part and inside of the second flexible mesh part and is provided with a plurality of openings, each opening being sufficiently small that microwave radiation is unable to pass through, wherein an outer sleeve and the inner mesh part each comprise a braided, woven, knitted or otherwise interlaced material which in use flexes as the threads of the interlaced material slide over one another, or move relative to one another and which may have high electric conductive surfaces, and wherein at least one of the first flexible support structure or second flexible support structure comprises at least one helical spring.

Description

(1) There will now be described, by way of example only, two embodiments of the present invention with reference to and as illustrated in the accompanying drawings of which:

(2) FIG. 1 is a cross section through a first embodiment of a guide in accordance with the present invention;

(3) FIG. 2 is a cross section through a second embodiment of a guide in accordance with the present invention;

(4) FIG. 3 is an (a) cross section and (b) end view of a flexible PTFE spring that forms a part of the guides of FIG. 1 or FIG. 2; and

(5) FIG. 4 shows a launcher connected to a vibrating receptacle for feedstock, the launcher including a guide as shown in FIG. 1 or FIG. 2.

(6) FIG. 5 is a photograph of a small section of braided material used to form a sleeve,

(7) FIG. 6 shows a modified spring that can be used within a further embodiment of a guide assembly according to the invention,

(8) FIG. 7 show an alternative combined sleeve and support structure that can be used within a guide assembly in accordance with the present invention,

(9) FIGS. 8(a) and (b) shows an arrangement for securing the PTFE spring and for adjusting the tension of the PTFE spring in the embodiment of FIG. 1 or FIG. 2; and

(10) FIG. 9 shows a still further alternative combined sleeve and support structure that can be used within an embodiment of the present invention.

(11) A guide 1 that substantially fails to transmit mechanical vibrations comprises a flexible tubular multi-layer waveguide that is terminated at each end with a flange 2, 3. The multi-layer waveguide has an effective internal diameter equivalent to a hollow waveguide of 89 mm although this can be varied according to the wavelength of the radiation that it is intended to guide, and the guide has a sufficiently different natural frequency of resonance to that of the vibrating source that it is able to isolate substantially all of the resonant frequencies emanating from the source. A structure with a resonant frequency of 0.5 Hz is thus able to act as a non transmitting barrier to frequencies of 50 Hz.

(12) In its simplest form the guide shown in FIG. 1 can be considered to comprise at least one sprung section which may or may not be electrically conductive and at least one electrically conductive mesh or textile section (textile meaning a woven or knitted or braided mesh material or other interlaced structure) Material selection for both the sprung and textile sections would take in account their hysteretic (material) damping properties, the natural frequencies of resonance of the component(s) and the combined strength of their elastic and viscoelastic properties

(13) In detail the guide 1 comprises an inner support structure in the form of a helical PTFE spring 5 machined from a solid billet or extruded into a helical coil as shown. The coil has a uniform diameter along its length in this example. As shown in FIG. 6 it may be provided with a metallic coating. FIG. 3 shows a suitable spring 4 in detail, where it can be seen that a helical slot 5 is cut into the wall of a hollow cylinder that extends from one end to the other continuously. The PTFE spring 4 may be integrally formed with two collars at each end enabling the spring to be secured to the flanges 2, 3 of the guide. An optional integral end portion 8 that closes one end of the cylinder is shown in dashed line. This end portion may comprise a solid PTFE window.

(14) The inner spring 4 is surrounded concentrically by an inner sleeve 9 of textile material comprising a woven braided copper tube. The inner wall 10 of the tubular sleeve 9 forms a continuous electrically conducting wall. The low dielectric loss PTFE is of sufficient tensile strength to substantially maintain the inner dimensions of the electrically conductive wall so that deformations of the wall which would otherwise create reflected power and/or mode variation are eliminated or minimised to an acceptable level according to the application. The manufacture of PTFE, stabilisation through sintering and machining of a compressed billet into a torsional spring is a known art. The precise choice of PTFE, the thickness of, the pitch of, and the number of coils and the number of starts in the spring are selected to achieve a flexural performance capability according to application, but the spring chosen preferably results in:

(15) 1. a sufficiently supported structure to maintain the electrically conducting properties of the inner sleeve

(16) 2. a sufficiently light and low tensioned structure to poorly transmit vibrations of frequencies generated by the source of vibration.

(17) 3. Non-transmission of vibration due to the viscoelastic (hysteretic) properties of the PTFE

(18) 4. Non-transmission of vibrations through the structure of the guide.

(19) The woven braided copper tube 9 is preferably seamless and made up of a plurality of braids which in turn are made up of a plurality of threads (filaments, wires.tapes) of a fine gauge. The braids 10,11 formed from threads 12 are shown in FIG. 5 for a small portion of the textile material. The braids pass repeatedly under and over other braids and are tightly woven.

(20) Weaving of continuous metal braids into a thin sheet material that can be configured as a three dimensional tubular structure is a known art and it is further known that these tubes can be used for their flexible qualities, but the weave chosen preferably results in:

(21) 1. a woven, knitted, braided or otherwise interlaced seamless tube wherein the copper wire has a sufficiently high surface coverage to contain the selected frequency of microwaves by ensuring that any gaps in the material between the threads and/or the braids at the absolute maximum limit of flexion are no bigger in diameter than a quarter of the wavelength selected to be propagated by the conducting surface.

(22) 2. A woven tube wherein the copper wire has a sufficiently high composite thickness of the electrically conductive wall that it represents many multiple skin depth lengths, as a minimum to prevent microwave leakage for the selected wave frequency and power

(23) 3. A woven tube wherein the direction of the woven braids follow a substantially helical path in relation to the axis of the elongate tube.

(24) 4. A sufficiently light and low tensioned structure to poorly transmit vibrations of frequencies generated by the source of vibration.

(25) It has been found that an electrically conductive sleeve (in this instance constructed from tinned copper wire) constructed to achieve the above requirements exhibits the capability to rapidly and repeatedly flex in multiple planes simultaneously due to interfacial slip at the numerous thread/braid interfaces, and the helical paths created by braids of the weave. A weave made by one braid lying parallel to the axis of the guide and the other weave lying at a right angle to the first, is more vulnerable to transmitting vibrations than a weave which is positioned with the braids lying on the bias in relation to the axis of the guide.

(26) The PTFE spring 4 and the woven tube 9 are secured in a spaced relationship relative to each other by means of the flanges 2, 3 at the two ends of the elongate cylindrical structure. Known means of attaching braided metal weave to flanges such as crimping, welding, brazing, soldering may be used, although in a preferred embodiment a suitably secured clamping mechanism may be used which allows for the structure to be easily disassembled and repaired.

(27) In the first example of FIGS. 1 to 3, each flange comprises a circular ring that has a hole bored through the edge 201. This is then tapped to allow a M8 size grub screw 202 with a tapered end to be fitted. Two such holes diametrically opposite one another give greater security.

(28) When in place, a further small bolt 203 with an anti-vibration washer 204 (such as Nordlock) is inserted so as to stop the grub screw from loosening due to vibration. The inside sleeve of the PTFE has a series of shallow indents into which the grub screw is secured. Tensioning of the PTFE spring may be adjusted by selection of indent into which the grub screw is tightened.

(29) It has been found experimentally in trials where this structure has been coupled to a vibrating item of processing machinery or other object, typically a container such as a trough, as shown in FIG. 4, that preferably the assembled structure comprises a second support structure comprising an outer support structure forming a spring 13. In this example, the spring is of the same material as the first PTFE spring 4 but of a sufficiently greater diameter that it can concentrically surround the first inner sleeve in a spaced relationship with the coil of the spring following an opposite helical path to that described by the first spring.

(30) Additionally, an outer sleeve of textile material comprising a second braided woven tube 14 is provided which may or may not be of the same material as the first braided woven tube but of a sufficiently greater diameter than the first braided woven tube so that it can concentrically surround the second spring 13 in a spaced relationship, the second spring and second sleeve being similarly attached to the two end flanges 2, 3.

(31) The flange holds the two springs in balanced torsion, maintaining the optimum degree of rigidity required to support the inner sleeve yet retaining sufficient flexibility to poorly transmit vibration from the vibrating source.

(32) This composite structure has been found to function as a vibration non-transmitting system in a dynamic environment. It is thought that this results from operating the vibrating unit at frequencies that are substantially different from the natural mechanical vibrational frequencies of the waveguide assembly . . . .

(33) In this embodiment it is notable that the two sleeves 9, 14 are separated from contact with one another by a PTFE component and an additional characteristic of the second braided tube is that it provides enhanced protection from any leakage of microwaves from the inner sleeve guide.

(34) An alternative embodiment of a guide 100 is shown in FIG. 2 of the drawings. In this embodiment, the components which are the same as those of the first embodiment are marked using the same reference numerals for clarity but increased by one hundred.

(35) The guide 100 includes an additional outer concentric component that comprises a flexible washable membrane 115 which prevents dust and oil particles in the external environment from becoming entrapped within the braided woven weave. In this embodiment a light PTFE bellows had been chosen. The bellow should not be so rigid as to prevent the sleeves deforming under vibration, as it would otherwise transmit from one end of the guide to the other.

(36) The guides 1, 100 may be used to launch microwave energy into a vibrating receptacle. For instance, the energy may be used in a launcher 200 to heat feedstock in the receptacle.

(37) In such an arrangement, as shown in FIG. 4 a launcher 200 is secured to a wall of a container 240. The container 240 is provided with a window 245 of material which is transparent to microwaves, and is aligned with one end of the guide 1,100 of the launcher 200. The flange 2,102 at the first end of the guide part is secured to the container 240 around the window and the flange at the other end 3,103 is secured to a rigid waveguide 230 which in turn is fixed to a source of microwaves 210.

(38) The container 240 is supported on a vibration stage 250 such as a bed (not shown) which is connected to a motor that upon rotation causes the container to vibrate. This vibration causes the guide to vibrate, but the guide isolates this vibration rather than transmitting into to the rigid waveguide 230 and so little vibrational energy is transmitted to the microwave source. This ensures the microwave source 210 is protected from damage that may otherwise be caused by vibration of the container.

(39) Also shown in FIG. 4 is a fan 220 which forms part of the launcher 200, the fan blows air from the rigid waveguide 230 (or from outside) into the guide 1,100. This air can pass along the guide and may escape through the gaps between the braids and individual threads of the sleeves. The air helps cool the inside of the guide, and also helps to prevent arcs that may be produced inside the guide. This is especially useful where there may be moisture in the guide on first firing up the microwave source which could produce arcs.

(40) In a modification, shown in FIG. 7 a sleeve 400 can be provided which is formed from a mesh of material that is woven or braided, with a supporting structure 420 that is integrated into the material. This supporting structure may be woven into the material to form a helical spring, perhaps using heavier gauge wire compared with the gauge of the rest of the mesh.

(41) In another alternative shown in FIG. 9, a spring 500 may be provided which is similar to the PTFE spring of FIG. 3 but which has mesh material 510 between the windings to prevent microwaves escaping through the spring. Again, this effectively combines the support structure and the sleeve in one element. As shown, the solid strip of the spring may be perforated to increase its flexibility. This feature could be used in the embodiments of FIGS. 1 and 2.

(42) In a modification to the invention, the guide may be provided that has a smaller internal diameter for a given microwave frequency so that it functions as a choke, the guide providing a means by which fluids (such as air) and/or solids can pass from one object to another whilst preventing the passage of microwaves, the guide absorbing vibrations to prevent them passing unattenuated along the guide.